Power transmission



p 2, 1941' E. L. ROSE 2,254,319

POWER TRANSMISSION Filed June 17, 1936 6 Sheets-Sheet 1 INVENTOR EDw/Iv L. Poss W g 7M v ATTORNEY SeptQZ, 1941. ROSE 2,254,319

' POWER TRANSMISSION Filed June 17, 1936 6 Sheets$heet 2 INVENTOR Enwuv L. Ros:

MA .M

ATTORNEY POWER TRANSMISSION Filed June 17', 1936 6 Sheets-Sheet 5 |NVENT OR Epwuv L. Ross ZZwzf/IM ATTORNEY Filed June 17, 1936 6 Sheets-Sheet 5 Bria/flat 1000 Z a. 600 I {/7 n: 600 a: *8 q PUMP a E k k if PUMP I00 'f7'- --f"-/ 1: PUMP MOTOR 80 E "J o k 4-0 a Sept. 2, 1941. E. L. ROSE 2,254,319

POWER TRANSMISSION LOAD IN TONS INVENTOR ATTORNEY Sept. 2,'1941. E SE 2,254,319

LBS. PER 50. IN.

POWER TRANSMISSION Filed June 17, 1936 6 Sheets-Sheet 6 400 PUMP REV. PEI? Mm} PUMP arm? 1 a0 I, 0 7'0 I00 LOAD ny 7'0/vs INVENTOR Eiuwnv L. Pose ATTORNEY Patented'Sept. 2, 1941 2,254,319 rowan TRANSMISSION Edwin L. ltosei'waterbury, Conn., assignor to The Waterbury Tool Company, Waterbury, Conn., a corporation of Connecticut Application June 17, 1936, Serial No. 85,629

7 Claims.

This invention relates to power transmissions and particularly to transmissions of the hydraulic type comprising a fluid pump and fluid motor either or both of which may be provided with mechanism for varying its displacement in order to vary the speed ratio betwen the prime mover which operates the pump and the load device which the motor operates. The invention is illustrated as adapted for use in a well drilling rig of well-known type in which a string of drill stem is caused to revolve by a rotary drilling head while a portion of the weight of the string rests upon the earth formation at the bottom of the hole being drilled, the remainder being suspended on a block and falls mounted in -a drilling derrick and connected to a draw-works drum. I o v In earth boring operations of this general class it is necessary from time to time as the work progresses to retract the drill stem from the hole for the purpose of replacing the cutting bit at the lower end of the drill stem. In so doing it is necessary to stop the rotational movement of the drill stem and hoist the stem a suitable distance to near the top of the derrick, this distance usually being 90 feet, and to grip the stem at the rotary table and remove the section of the drill stem projecting above the table. The hoisting apparatus is then lowered and connected to the remaining portion of the stem projecting from the rotary table and hoisted another 90 feet and the operation is repeated until the entire string is removed from the hole. After necessary repairs to the bit are made, by reversing this process the bit may be again brought to working position at the bottom of the hole.

For a given maximum horsepower of the prime mover and a given weight of drill string there is only one speed ratio between the prime mover and the draw-works drum which will permit the string to be retracted at a speed which utilizes the full power of the prime mover. It is obviously impractical to provide direct mechanical gearing between the prime mover and the drawworks drum with s'uflicient speed ratios to permit full power hoisting of the stem at each 90- foot hoist. In drilling rigs in general use heretofore variable speed chains and sprockets or spur gearing have been provided with usually 4 or 6 available speed ratios and the operator has selected the highest drive ratio which will permit the prime mover to hoist the stem without stalling. With this construction it is necessary to use one speed ratio for a considerable number of consecutive hoists of the drill stem before the drill stem weight is reduced sufiiciently to enable the operator to shift to the next higher can be utilized only on the first hoist at a given down to its intended depth in the least possible total lapsed time. Inasmuch as normal drilling operations are suspended while the drill string is being retracted and replaced for repair purposes, it is essential to keep the time consumed for this purpose to a minimum and it is customary to provide prime movers of severaltimes the power output required for drilling operations so that the string may be retracted at a maximum speed and lost time reduced to a minimum. It will be seen that in retracting the string the weight of the string and the load to be lifted is progres ratio and that thereafter the power load on the prime mover progressively decreases.

It is an object of the present invention to provide a draw-works drive for a well drilling rig whereby the ratio of power transmission between the prime mover-and the draw-works drum may be adjusted to the value necessary to utilize the full power output of the prim mover at each hoist of the drill stem.

' A further object is to provide a draw-works drive of such character wherein an operator-controlled member may be moved to cause the drawworks drum to rotate in hoisting direction and wherein automatic means beyond the control of mining the size of'fluid pump and fluid motor necessary to transmit a given horsepower over any selected range of speed'ratios, there are certain important limiting factors which have heretOfOre prevented full utilization of this type of power transmission, particularly in applicationsrequiring the transmission of a constant horsepower over a wide range of speed ratio variation.

A further object of the present invention is to provide a hydraulic power transmission which is operable at constant horsepower over a considerably wider range of speed ratios than has heretofore been possible under a similar set of conditions.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of the present invention is clearly shown.

In the drawings: a

Fig. 1 is a plan view of a well drilling rig embodying a preferred form of the present invention.

Fig. 2 is a longitudinal cross section of a variable speed hydraulic transmission employed in the apparatus illustrated'in Fig. 1.

Fig.3 is a diagrammatic view of a hydraulic control circuit associated with the power transmission of Fig. 2. 1

Fig. 4 is a cross section on line 4-4 of Fig. 2.

Fig. 5 is a cross section on line 4- of Fis. 6.

8! driving a drill stem through the medium of the usual Kelly and the draw-works drum It Fig. 6 is a side view of a portion of 'the hyart methods of operating at constant horsepower.

Fig. 9 is a plot similar to Fig. 8 illustrating the operating characteristics of the present invention.

Referring now to Fig. 1 there is illustrated a draw-works ll having a main drum I! mounted in bearings i4 adapted to be driven through a jaw clutch l8 and a chain and sprocket drive It. The drawsworks may be provided with brakel bands 20 and with the other usual accessory apparatus thereto suchas cat-head shaft, etc., not illustrated. The draw-works preferably comprises but a single sprocket and chain drive I. between the drum l2 and a fluid motor 22 having an output shaft 24 with which the chain and sprocket drive is directly connected. A fluid pump 26 is associated with the motor 22 in a manner to drive the same so that the pump and motor together comprise a variable speed hydraulic transmission. The pump 28 has an input shaft 28 on which is mounted a pulley forming part of a multiple belt drive 3| by which power is transmitted from a power shaft 32 to' the pump shaft 28.

The power shaft 32 is connected to the output shaft of a prime mover 34, for example a Diesel engine, through the medium of'a jaw clutch 38 and is also adapted to be connected through a jaw clutch It to a multiple belt drive by which the shaft fl may be driven from'a second Diesel having wound thereon the cable line by which the drill stem is raised and lowered through the usual block and falls rigging. The slush pumps 44 and 48 are connected by suitable piping and .valves, not shown, to the mud circulating system by which mud is circulated downwardly through the hollow drill stem to the cutting bit and returned around the outside of the stem to a mud reservoir.

In determining the size of the fluid pump It and fluid motor 22 which is necessary to transmit a given constant horsepower over any selected range of speed ratios, the design of the pump ,and motor impose certain limitations which haveheretofore required the use of a prohibitive size hydraulic transmission for an application such as the draw-works drive of the present invention. Any given design of transmission has a limit both to the speed at which it may be operated and the working pressure to which it may be subjected. Such transmissions are usually rated at the maximum speed for safe operation at maximum working pressure. The permissible speeds at lower working pressures are considerably higher, however, although as will be explained hereafter prior constructions have been of necessity limited to the maximumspeed for safe operation at maximum working pressure.

Referring now to Fig. 8 there is represented two plots of typical operating conditions as applied to a hydraulic transmission for a drawworks drive wherein the load in tons of drill stem or equivalent weight which the hoist drum must lift through the block and falls is plotted horizontally while the pump and motor strokes in per cent, pump and motor speed in revolutions per minute, and operating pressure in pounds per square inch are plotted vertically. It be seen that the load in tons and consequerrtly the torque on the output shaft of the hydraulic motor varies over a range of 5 to 1, that is the maximum load is flve times the minimum. If the weight is to be raised at a speed which requires the. same horsepower for any weight of drill stem, the speed of the hydraulic motor necessary for any given weight of drill stem is represented by the composite solid and dot-dash curve of motor speed. This curve is such that at any point thereon the product of the horizontal coordinate, that is the load in tons, by the vertical coordinate, that is the speed in revolutions per minute, is a constant value. As a numerical example, neglecting losses. for 303 horsepower the speeds indicated on the plot require a ratio between the motor and the drill stem of 3.5 revolutions per foot of-vertical mo- 4 tion of the drill stem so thatstarting from the engine prime mover 42. The shaft 32 is adapted ing table 68. The draw-works l0 and the drilling table 68 are preferably mounted adjacent the base of a drilling derrick, not shown, the table bottomof a finished hole with tons of drill stem, 303 horsepower will be required to raise the stem at 50 feet per minute or revolutions per minute of the motor shaft while at the lightest load of 20 tons represented by the per square inch, and the minimum motor speed as 175 revolutions per minute. The range of speed ratios required, namely Sto 1, requires a range of stroke variation in either the pump or the motorbetween 20% and 100%.

Inoperating a transmission of this character at constant horsepower over the range of speeds indicated, two methods of varying the speed are available. The first method, and the more usual one, is by varying the pump displacement in proportion to the speed required for any load, while the motor displacement remains fixed. The various conditions of operation by this method are indicated by the dot-dash lin'es in Fig. 8. It will be noted that starting at the right of the figure with 100 tons load, the working pressure is at the limit of 1,000 pounds per square inch and that in order to get the to 1 range in speeds the pump must be run at 20% stroke for a motor speed of 175 revolutions per minute necessitating a pump speed of 8'75 revolutions per minute for all loads. The limiting condition with such operation is at the-right hand side of the plot wherein the pump running at the high speed of 875 revolutions per minute is subjected to pressures in the neighborhood of 1,000 pounds" per square inch, which is beyond the safe operating pressure at that speed. In other words, the

variable displacement pump portion of the hydraulic transmission is subject simultaneously to peak operating speed and peak pressure when the drill stem load is near its upper limits.

The other method of operation by which con-' stant horsepower may be transmitted over the selected range in speed ratios is by using a constant displacement pump and a variable displacement motor. The conditions for this method are plotted in Fig. 8 by solid lines from which it will be seen that the limiting condition motor displacement and variable pump displacement over one range of load and with fixed pump displacement and variable motor displacement to 50% at 100 tons by suitable control mechanism,

the pump may be operated at approximately the speed necessary to raise 50 tons load with 303 horsepower which is 350 revolutions per minute in the example selected. In this range of operation the operating pressure increases from 500 pounds per square inch at 50 tons load to 1,000

4 pounds per square inch at 100 tons load. It will be noted that at peak operating pressure the pump is operating at a comparatively low speed of approximately 350 revolutions per minute. In

the range of from -20 to tons load, the pump displacement is maintained fixed at 100% and the motor displacement reduced from 100% to 40%, thus raising the motor speed as the load decreases to approximately 875 revolutions per minute at 20 tons load. In this range of operation the working pressure is constant at 500 pounds per square inch so that when the motor is operating at the high speed of 875 revolutions per minute, itis'su ected to only half the maxiso far as simultaneous high speed and high pressure are concerned is at the left-hand side of the plot where the motor speed is high at 875 revolutions per minute and the. pressure is likewise high, being maintained constant at 1,000 pounds per square inch throughout the full operation. In addition, in order to cover the full range of speeds it is necessary for the motor stroke to reach in this instance a low value of 20% which is so close to the friction angle as to make such operation unfeasible due to the extremely low efliciency at such small motor strokes. It will, therefore, be seen that neither of these methods of operating at constant horsepower over the 5 to 1 range of speed ratios is satisfactory since both require operation of the transmission with simultaneous imposition of maximum operating pressure and maximum operating speed on one of the units of the transmission. For satisfactory operation with either method it is necessary to at least double the size of machine having the same limits of pressure and speed whereby either the peak speed or the peak pressure or both may be reduced and still transmit the required horsepower. The size actually necessary in a typical drilling rig installation for such operation is entirely prohibitive from the standpoints of bulk and weight as well as first cost with transmissions of the best speed and pressure ratings at present available.

According to the present invention these diflioulties are avoided and the size of machine necessary to satisfactory-operation is considerably remum operating pr ssure.

In making the ransition from one range of operation to the ther, it is necessary to provide some means for transferring the control from one mechanism to another. This is preferably accomplished by operating at 100% stroke on both the. pump and the motor over a small range of load, for example from 49 tons to 51 tons and causing the prime mover to fall off in speed slightly as the load increases over this range. It

will be seen that with this method of operation neither the pump nor the motor is subjected simultaneously to maximum operating pressure at maximum speed so that the preformance of a given size transmission at constant horsepower is extended over a far greater range than ble by other methods of operation.

Referring now to Figs. 2 and '7' the power transmission and control system therefor includes a stroke varying hydraulic motor 10 for the variable displacement pump 20 and a stroke varying hydraulic motor 12 for the variable displacement motor 22. The motor 22 and pump 26 are illustrated as of the well-known Waterbury construction comprising revolving cylinder barrels I4 within which pistons 16 are reciprocated by the motionof socket rings 18 which re volve in tilting boxes and 82. The tilting box 80 carries a stud 84 having a pivoting and sliding connection with a differential piston 86 mounted in cylinder bores 88 and 90 of the hydraulic m0- tor10. The bore 90 is subjected to a constant fluid pressure from an auxiliary pump 92 through a conduit 93 while the bore 88 is subjected to either pressur from the pump 92 or to atmospheric pressure in accordance with the movement of certain control valves later to be described.

The tilting box 82 carries a stud 94 having a pivoting and sliding connection with a differential piston 96 reciprocable in bores 90 and I00 of the fiuid motor I2. The bore I00 is subjected to constant pressure from the pump 92 through possia; conduit IOI' while the bore 9a is subjected either to auxiliary pump pressure or to atmospheric pressure in accordance with the movements of a pressure responsive pilot valve I02.

A movable valve member I04 of the pilot valve 3, whereby the side of the working circuit which is of higher pressure at any instant is placed in communication with the lower end of the bore I00. An adjustable spring IIO urges the valve member I04 downwardly against the pressure exerted in the lower end of the bore I00. A passage I20 is normally closed by the piston H2 and is open to the atmospheric pressure at the interior of the case of the motor 22 through a passage I22 when valve member I04 moves downwardly while communication is established between passage I20 and the auxiliary pump through a conduit I24 when the valve I04 is moved upwardly.

The fluid motor I is under the control of a manually operable valve I20 which is normally biased to neutral position by centering springs I28. Valve I20 is provided with a central bore I30 within which a pair of piston heads I02 and I34 may be moved to place a conduit-I00 in communication either with a conduit I00 leading from the outlet of the auxiliary pump 02 or with a conduit I40 leading to the atmospheric pressure side of the system. In series with the valve I20 formed in piston I and the body of the valve 9 I42 respectively. The piston has a projecting stem I52 which is operatively connected to an arm I54 of a speed governor I which may be of any well-known construction and forms no part of the present invention per se.

A third valve I00 is provided having a bore I00 within which a piston valve I02 reciprocates and controls communication between a conduit I04 leading to the bore 00 and either the conduit I00 or the interior of the casing of the pump 20 through a conduit I00 formed in the piston valve. I02. A conduit I00 communicates between the lower end of bore I00 and the shuttle valve IIO while an adjustable spring I10 similar to the spring I I8 of valve I02 serves to make the piston I02 responsive to the pressure in the main working circuit. For the purpose of maintaining the motor shaft stationary when the tilting box 00 of the pump 20 has beenbrought into the vicinity of zero stroke without requiring tedious manual adjustment to prevent creeping of the motor shaft, means is provided for directing fluid from the auxiliary pump 02 to the main working circuit of the transmission as required to maintain the motor shaft stationary. For this purpose an anti-creep valve I12 is provided at one end of the casing of the fluid motor 22. Valve I12 comprises a central bore I14 within which is slidably mounted a duplex piston valve I10 for controlling the admission of pressure fluid from the conduit I10 through either a conduit I00 leading to one valve port' I02 of the hydraulic transmission or to a conduit I04 leading to the other valve port I00 of the transmission. Valve "0 also controls communication between an exhaust conduit I00 and branches I00 and I32 of the conduits I00 and I04 respectively. Exhaust conduit I00 leads 'to a port I04 formed in the bore 00 of the fluid motor I0 and with the tilting box in the neutral position illustrated registers with a passage I00 formed in the piston 00 so that when the tilting box 00 is in or near neutral position passage I00 is in open communication with the interior or the casing of the pump 20.

The conduit I10 leads to a port I00 formed in the bore I00 01' the valve I20. An auxiliary piston 200 of the valve I20 controls communication between the port I00 and a port 202 leading from the auxiliary pressure conduit I30. The pistons I34 and 200 are adapted to close communication between the ports I00 and 202 whenever the valve I20 is moved out of neutral position suiilciently to open communication between the conduit I30 and either the conduit I00 or the'conduit I40.

The auxiliary pump 02 is driven from the shaft 20 of the pump 20 by a belt drive 204 (Fig. 6) while the speed governor IE0 is driven from the pump 02 through a belt drive 200. The valve H2 is operated in accordance with the direction of movement of the motor shaft 24 through a spring loaded friction clutch 200 (Fig. 2) having a driven ring 2I0 which carries a stud 2I2 having apivoting and sliding engagement with piston Ill. The interior of the casings of the pump 20 and the motor 22 and the inlet side of the pump 02-are in open communication with an expansion tank 2 as is well known in the art. A relief valve 2I0 is provided for limiting the pressure developed in the outlet conduit of the auxiliary pump 02.

The speed governor I00 is so adjusted as to raise the valve I40 upon a decrease in speed below the speed corresponding to the maximum power speed of the prime movers 34 and 42 and to lower the valve to the position illustrated upon an increase to that speed. The spring N0 of the valve I00 is adjusted to hold the valve downwardly in the position illustrated at all safe normal operating pressures within the main working circuit of the transmission I and to permit the valve I02 to move upwardly only when safe operating pressures are exceeded. For the example illustrated in Fig. 9 this setting would be just over 1,000 pounds per square inch. The valve I 02 is adjusted to regulate to a pressure corresponding to that developed at full stroke of the motor and full stroke or the pump, that is in the example illustrated in Fig. 9, 500 pounds per square inch. The sensitivity of the speed governor I00 is preferably much less than the sensitivity of the speed governors which are customarily provided on Diesel engines 34 and 42 so that the engine governors are permitted to respond fully to any change in speed before the governor I00 exercises control over the valve I42.

In operation of the device as used for hoisting drill stem the clutches 30 and 30 will both be engaged so that the two engines 34 and 42 are compounded to drive the shaft 32. The clutches .02 and 04 will both be disengaged so that the slush pumps 44 and 40 will be stopped and the clutch 00 will be disengaged so that the pump 00 and the motor 04 will not be operating. with clutch I0 engaged the operator may the valve I42.

move the control handle 2I8 to move the valve I26 to the right in Fig. 3 closing off communication between the ports I98 and 282 and openin communication between the conduits I36 and I38. Assuming thestring of drill stem to be the full length of a nearly completed well and that the weight to be lifted is in the range between 50 and 100 tons, the auxiliary pressure fluid admitted from the conduit I38 passes through the valve I26 through the conduit I36 and to Since at the instant this path is opened, the tilting box 88 is in neutral position, the engines 34 and 42 will be idling so that the valve I42 is in the down position, the fluid is permitted to pass through the conduit I48, whence it passes through valve I58 to the cylinder 88. The valve I58 will be in its lower position at this time due to the lack of excessive pressure in the inain fluid circuit of the transmission.

The piston 86 is therefore moved to the right increasing the stroke of the pump 26 until a value is reached such that the speed at which the drill stem is being hoisted is suificient to impose the full power load on the engines 34 and 42. For purposes of comparison it may be assumed that the pump shaft 28 is rotating, top away from observer in Figures 2 and 6, and thus this movement of the tilting box causes fluid to be delivered into port I82 and withdrawn from port I86. This in turn rotates the motor shaft 24 in the opposite direction. Further movement of the piston 86 to the right beyond this point will cause the engines 34 and 42 to slow down somewhat thus causing the governor I56 to lift the valve I42 and connect the conduit I48 to the exhaust through conduits I49 and I58. The valve I42 thus limits the movement of the piston to the right and thereby regulates the stroke of the pump 26 to the proper value necessary to maintain the constant peak horsepower speed at the prime movers 34 and 42. The drill stem is accordingly raised at the fastest possible speed and as the top of the stem approaches the top of the derrick, the operator will move the handle 2I8 fully to the left thus opening communication between the conduits I36 and I48. The cylinder 88 is thereby connected to the exhaust through conduit I64, valve I58, conduit I48. valve I42, conduit I36, valve I26 and conduit I48. The auxiliary pump pressure constantly exerted in the cylinder 98 forces the piston 86 to the left bringing the tilting box 88 into the vicinity of neutral position.

As the operator sees that the drill stem is stopping he releases the handle 2I8 permitting it to move to neutral position wherein the conduit I36 is blocked and communication is established between the ports I98 and 282. The anticreep valve I12 thereupon operates to connect the main circuit of the transmission to the outlet of the auxiliary pump 92 and to the exhaust side of the system in the proper direction to counteract any small rate of fluid delivery by the pump 26. Thus, if the pump tilting box should be out of neutral slightly, in a position tending to cause the shaft to rotate counterclockwise in Figure 3, the valve I16 will be slowly moved to the left until a connection is established between conduit I16 and conduit I84, thus admitting pressure oil from the auxiliary pump 92 through conduit z'l38, ports 282 and I88 of valve I26, conduit I18, valve I12, conduit I84, to the port I82 of the main transmission. As the valve I16 continues to move to the left, the

gressively increased as is also the opening between conduit I98 and conduit I14. The effect of the increased opening at conduit I84 is to increase the pressure applied to port I82 by the auxiliary pump 92. The effect of the increased opening at conduit I98 is to decrease the pressure applied to port I86 by the main pump 26. As soon as a point is reached where these two pressures are equal, the motor 22 will cease to turn, and the valve I16 will remain in its adjusted position.

It will be understood, of course, that when the operating handle 2I8 is first released and the pump tilting box brought to approximate neutral position, the shaft 24 will have been turning, and that the spool I16 will lie on either one side or the other of neutral position depending upon whether the handle 2I8 Was-released from a hoisting or from a lowering position. As soon as the pump tilting box reaches nearly neutral position, however, port I96 is opened, thus permitting the pressure in ports I82 and I86 to become balanced as above described. It will be seen that, should the valve spool I16 be in its extreme lefthand position when the handle 2I8 is released, and when port I96 opens to port I94, then the conduit I84 will be wide open and will produce a higher pressure in port I82 than the pump 26 produces in port I86. Thus the motor 22 will tend to rotate clockwise shifting the'spool I16 to the right until the balance of pressures in. thetwo main ports is again achieved. The draw-works is thus maintained.

stationary until-such time as the operating handle 2I8 is again operated.

During the raising of the drill stem at constant horsepower as above described the valve I82 is lifted soon after the tilting box 88 leaves neutral position and inasmuch as the operating pressure for loads above 50 tonsis above 500 pounds per square inch, the valve I82 will remain in the upward position and tilting box 82 will be moved immediately to full stroke during the entire period of hoisting, and so long as the weight of the stem is on the draw-works drum I2.

The stem may be inched down by a small movefor hoisting.' Since the load is negligible in lowering the hook, the motor 22 remains at minimum stroke and the speed of lowering is thus at maximum. With loads near the upper limit of 100 tons the rate of travel of piston 86 may cause acceleration of the drill string at a rate which wouldyimpose excessive pressure on the system. Likewise, should the drill stem become caught in the hole for any reason, excessive pressures may be developed. Whenever, due to any cause, the working pressureexceeds the safe value, valve I62 is lifted against spring I18 thus exhausting fluid from cylinder 88. until a safe operating pressure is reached.

As each section of drill stem is removed from the string the piston 86 moves further to the piston 86. When the-weight of the drill string reaches approximately 51 tons, the piston 40' moves to the right to its full stroke. Thereafter for one or two successive hoists the transmission operates at 1 to 1 ratio and the speed of the prime movers 34 and 42 is permitted to increase slightly while the operating pressure in the main transmission circuit drops to 500 pounds.

As the drill stem weight further decreases, the valve I02 comes into operation and prevents the working pressure from dropping below 500 pounds by decreasing the stroke of the motor 22 as required to maintain the operating pressure at that value. Thus, as soon as the operating pressure drops to 500 pounds the spring I I8 is able to overcome the force of the fluid in the lower end of the bore I08 and move the valve I04 downwardly thus opening the cylinder 08 to the exhaust side of the system through conduits I20 and I22. The auxiliary pump pressure constantly exerted at the cylinder I thus moves the piston 80 to the right decreasing the stroke of the motor 22 until the operating pressure is maintained at 500 pounds. As successive sections of the string are removed, the piston 90 is moved further and further to the right until at the minimum load on 'the draw-works drum of 20 tons the motor is brought to minimum stroke of 40%.

At this point. the cutter bit may be removed and replaced and the drill stem fed back into the well according to the usual procedure of dropping it by disengaging clutch I0=and stopping it with the brakes 20. The empty hook may be raised at maximum speed by operating the control lever 2I8 as previously described. When the entire string has been again fed into the well, one of the clutches 52 or 04 may be engaged to start one of the slush pumps and the clutch 08 engaged to start the rotary table 08. Adjustment of the speed of rotation of the table 08 may be accomplished by manually operating the stroke regulator of the pump 00. The feeding of the drill stem into the hole as drilling proceeds may be taken care of in any of the usual manners, such as by holding a portion of the weight of the stem on the brakes 20.

If desired, the lowering of the drill string into the hole may be accomplished by using the hydraulic transmission and the Diesel engines to retard the fall of the string instead of the brakes 20. For operation in this manner, when a section of drill stem has been attached to the string,

the handle 2I8 is moved slightly to the right to "inch" the string upwardly, releasing the slips.

The handle 2I8 is then moved to the left connecting conduit, I30 to the return conduit I40. Fluid is thereby released from the bore 88 through conduit I04, valve I08, conduit I48, valve I42, conduit I30, valve I20, and conduit I until either the\pump 20 is brought to full stroke in a lowering direction or until the handle 2I8 is re-' turned to neutral position. The drill s m thus descends under its own weight, the Desel endecreasing the mechanicaladvantage of the drill string over the prime movers and thus multiplying the braking eiIect thereof. With a drill string weight of less thanflfty tons the motor stroke is maintained at a value less than full stroke and such that five hundred pounds per square inch pressure is maintained in the system as a result of the operation of the valve I02. During the retarding portion of the lowering cycle the pressure will tend to rise due to the increased force required to decelerate the drill string so that the motor stroke will increase. This further tends to decrease the mechanical advantage of the drill string over the prime movers. With a drill string weight of over fifty tons the motor is always at full stroke whenever the weight of the drill string is on the drum so that the reserve braking eflort which can be carried through the transmission is in proportion to the difference between the pressure created by the drill string weight and the pressure at which valve I08 lifts. At loads near the upper limit the lever 2I8 must be operated to the right for retarding the fall at an earlier point than with lighter loads. If desired the brakes 20 may be used to assist the prime movers in stopping the load at the end oi. the descent.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows: I

- 1. In a varlabl d power transmission system the combinati n of a prime mover, a variable displacement p driven by the prime mover, a variable displa ent motor driven by the pump, a load device driven by the motor and imposing a variable torque load thereon, means responsive to load variations for varying the pump displacement while maintaining the motor displacement constant in a manner to maintain a substantialdisplacement constant in a manner to maintain a substantially constant power load on the prime mover over another range of load torque at th motor.

2. In a variable speed power transmission system the combination of a prime mover, a variable displacement pump driven by the prime mover, a variable displacement motor driven by the pump, a load device driven by the motor and imposing a variable torque load thereon, means for varying the displacement of the pump, means for varying the displacement of the motor, and a load responsive control system for both said means operable to cause the motor speed to vary with load torque at the motor in a manner to maintain a substantially constant power load on the prime mover.

3. In a variable speed power transmission system the combination of, a prime mover, a. variable displacement pump driven by theprime mover, a

variable displacement motor driven by the pump,

' of fluid to the first motor for maintaining the substantially constant power load on the prime mover over another range of load torque at the motor.

4. In a draw-works drive for a well drilling rig the combination of a prime mover, a drawworks drum, a fluid pump driven by the prime mover, a fluid motor driven by the pump and driving the draw-works drum, operator controlled means for controlling the delivery of fluid to the motor, and means responsive to movement of themotor and automatically operative upon movement of the operator controlled means to drum-stopping position for directing fluid to the motor in a manner to bring the drum to restfrom a slow speed operation.

5. In a variable speed power transmission system the combination of a prime mover, a variable displacement pump driven by the prime mover,

a fluid motor driven by the pump, a load device driven by the pump, a second fluid motor for varying the displacement of the pump, a valve movable between three positions in the first of which the second motor is rendered operative to vary the pump displacement in one direction in the second of which the second motor is rendered operative to vary the pump displacement in the opposite direction and in the third position of which the fluid motor is non-responsive to said valve, a second valve responsive to the direction 01' movement ofthe first motor and connections between said valves whereby when the first valve is in the third position the second valve is rendered operative to control delivery first motor stationary.

6'. In a variable speed power transmission the combination of a prime mover, a pump driven by the prime mover, a fluid motor driven by the pump, a load device driven by the motor, means for controlling the flow of fluid delivered by the pump to the motor, an anti-creep valve operated in accordance with the direction of movement of the motor for causing operation of the motor oppositely to the movements causing operation of the anti-creep valve, and means connected for concurrent operation with the flow controlling means for inhibiting effective operation of the anti-creep valve when the flow controlling means is operated to cause'movement of the motor.

7. In a variable speed-power transmission sys- I tem the combination of a prime mover, a variable displacement pump ,driven by the prime mover, a fluid motor driven by the pump, a load device driven by the motor, a second fluid motor for varying the displacement of the pump, a means for controlling the flow of pressure fluid to said second motor, an anti-creep valve operated in ac-' cordance with the direction of movement of the first motor for directing fluid to the first motor in a direction opposite to the movements causing operation of the anti-creep valve, and means connected with the flow' controlling means for 

